In electrophotography, generally, a latent image bearing member composed of a photoconductive light sensitive material body is charged by corona discharge etc., then a charged latent image bearing member is exposed by laser, LED, etc., and the resulting electrostatic latent image is developed and visualized using a developer such as a toner to form an image with high quality.
Heretofore, latent image bearing members equipped with a photosensitive layer composed of an organic photoconductor (OPC) have typically been used as the latent image bearing member used in the image forming method. However, in recent years, a latent image carrier unit equipped with a photosensitive layer composed of amorphous silicon has been investigated in response to the requirement to improve the durability of image forming apparatuses. Although the latent image bearing members are abraded through sliding or fractioning with materials to be printed or elastic blades described later, since the amorphous silicon shows a very excellent abrasion resistance, higher durability of image forming apparatuses may be achieved from the viewpoint of abrasion resistance of the latent image bearing members. Specifically, the reduction speed of film thickness of the amorphous silicon due to abrasion is no greater than 1/100 of that of organic photoconductors.
Therefore, in the image forming apparatuses having a positively chargeable latent image bearing member equipped with the photosensitive layer composed of amorphous silicon, the latent image carrier unit (photoconductor) can show a longer operating life, and thus the imaging cost per image may be reduced. From the viewpoint of such advantages, use of the latent image bearing member equipped with the photoconductive layer composed of amorphous silicon has been spreading.
In addition, when a toner has remained on a surface of the latent image bearing member equipped with the photosensitive layer composed of amorphous silicon after images of the toner are transferred on a surface of material such as papers to be printed, the toner is removed by a cleaning unit. In regards to the cleaning unit, those equipped with an elastic blade have been widely used since the configuration is simple due to a small number of moving parts and thus the image forming apparatus can be downsized.
In this way, the latent image bearing member equipped with the photosensitive layer composed of amorphous silicon and the cleaning unit equipped with the elastic blade are often used in combination in view of the respective advantages.
However, there is a defect in the latent image bearing member equipped with the photosensitive layer composed of amorphous silicon in that the friction coefficient at the surface of the latent image bearing member tends to increase under prolonged and continuous formation of images. When the friction coefficient has increased, in the image forming apparatuses having the combination of the latent image bearing member equipped with the photosensitive layer composed of amorphous silicon and the cleaning unit equipped with the elastic blade, there arise a problem in that curling of the elastic blade or image defects (called as “void”) due to the resistance of toner particles to separate from the surface of the latent image bearing member tends to occur.
In order to solve the problems in the image forming apparatuses having the combination of the latent image bearing member equipped with the photosensitive layer composed of amorphous silicon and the cleaning unit equipped with the elastic blade, a method has been proposed in which a lubricant with a particle diameter of 1 μm or less is coated on the surface of the latent image bearing member by a lubricant supply means such as a brush.
However, in this method, the additional lubricant supply means such as a brush is necessary, and thus there are problems that downsizing of the image forming apparatuses is disturbed and also production cost of the image forming apparatuses is increased.
It may be envisaged that the lubricant is included into a developer containing a toner as the method to supply the lubricant to the surface of the latent image bearing member without the lubricant supply means. However, since fatty acid metal salts suited to lubricant particles are of negative charge, the charged amount of the toner is likely to decrease when the fatty acid metal salts are included into the developer containing a positively chargeable toner. Moreover, fine particles with a particle diameter of 1 μm or less tend to adhere to the surface of toners, therefore, when the positively chargeable toner and fine particles of fatty acid metal salts are used in combination, because a negatively charged toner generates, the toner is likely to scatter from development devices, and image defects such as fog tend to occur in the resulting images.